"We are looking into the reasons [for the loss]. We can confirm we have not lost any attack helicopters."

Earlier, Libyan state TV aired footage of what it said was an Apache helicopter shot down by pro-government forces in the western district of Zlitan.

Nato deployed Apache attack helicopters in Libya earlier this month during its UN-sponsored mission to protect civilians from forces loyal to Col Gaddafi.

Nato officials have not identified the exact type of drone helicopters being used, but analysts say the alliance has been operating the MQ-8 Fire Scout helicopter drone, made by US firm Northrop Grumman.

The drone is the first aircraft reported lost by Nato over Libya since it took over the no-fly mission on March 31.